In recent years, there are increasing demands for miniaturizing semiconductor devices along with the increase in the degree of integration, functionality and speed thereof. Accordingly, there are increasing demands for realizing an ultra-shallow semiconductor region formed by implanting a substrate with an impurity. Under such circumstances, plasma doping has been drawing attention as a technique with which it is easier to form an ultra-shallow semiconductor region implanted with an impurity, as compared with ion implantation widely used in the prior art as a technique for implanting a substrate with an impurity. With plasma doping, by exposing a substrate directly to a plasma, it is possible to implant an impurity in the plasma into the substrate without drawing the impurity out of the plasma. Thus, not only impurity ions in the plasma, but also electrically neutral impurities such as radicals or gas constituent atoms or molecules (hereinafter referred to simply as a “gas”) in the plasma can be implanted into the substrate in large quantities with a low energy. Therefore, as characteristics of plasma doping, it is widely known that
1. since the rate at which the impurity is implanted into the substrate is very high, the throughput is very high as compared with ion implantation; and
2. since the impurity implantation energy can be set very low, it is easy to implant an impurity into an ultra-shallow region.
By utilizing the first characteristic of plasma doping that the implantation rate is very high, an impurity can be implanted into the polysilicon gate with a very high throughput (see Shu Qin, Allen Mc Teer, Device Performance Evaluation of PMOS Devices Fabricated by B2H6 PIII/PLAD Process on Poly-Si Gate Doping, International Workshop on Junction Technology, p 68 (2006) (hereinafter referred to as “Non-Patent Document 1”)).
It has been reported that by applying the second characteristic of plasma doping that the implantation energy can be set very low, in combination with the first characteristic, a source/drain extension region which is a region substantially thinner than the gate can be formed with a low resistance (see Y. Sasaki, et al., B2H6 Plasma Doping with “In-situ He Pre-amorphization”, Symp. on VLSI Tech, p 180 (2004) (hereinafter referred to as “Non-Patent Document 2”) and Nuclear Instruments and Methods in Physics Research B 237 p 41-45 (2005) (hereinafter referred to as “Non-Patent Document 3”)).
Moreover, a technique has been recently proposed in the art which, in addition to realizing an ultra-shallow source/drain extension region with a low resistance, can control the uniformity in the impurity dose, which has been considered in the prior art as an important problem in putting into practice the formation of an ultra-shallow impurity region by plasma doping, as precisely as required for the source/drain extension region (see IIT(2006)524AIP866 (hereinafter referred to as “Non-Patent Document 4”), International Publication WO06/064772 pamphlet (hereinafter referred to as Patent Document 1″) and International Publication WO06/121131 pamphlet (hereinafter referred to as “Patent Document 2”)).
With regard to the dose controllability, which is another important problem in putting into practice the formation of an ultra-shallow impurity region by plasma doping, a technique has been disclosed in the art for suppressing the deposition of electrically neutral impurities such as radicals and the gas on the substrate (see United States Patent Application Publication No. 2006/0099830 (hereinafter referred to as “Patent Document 3”)). Patent Document 3 states that by measuring only the implantation dose of impurity ions with Faraday cups, it is possible to identify the dose and to thereby enhance the dose controllability.
As a technique that actively utilizes electrically neutral impurities such as radicals and the gas in plasma doping, a technique has been disclosed in the art in which a thin semiconductor film is formed on an insulative substrate, and then a thin impurity film is formed so as to be in contact with the thin semiconductor film, wherein the primary component of the thin impurity film is impurity atoms that can be electrically activated into carriers in the thin semiconductor film (see International Publication WO05/034221 pamphlet (hereinafter referred to as “Patent Document 4”)).